This invention pertains to rotary valves operable as either a three-way valve or a four-way valve for either advance or retraction of an operative member, such as a cylinder, and with there being a neutral position with the connections to the cylinder blocked and with there being free flow from the pump through the valve to reservoir.
A prior structure of applicant is shown in McClocklin U.S. Pat. No. 3,892,259, granted July 1, 1975, which shows a rotary control valve operable as either a three-way valve or a four-way valve.
Other valves of this general type are shown in Masuda U.S. Pat. No. 3,556,151 and Schultz U.S. Pat. No. 3,677,295. The first of these patents discloses valve structures wherein an added plate is provided to reduce leakage problems. The second of these patents has a construction wherein the rotatabe valve member has a pair of passages, each having a check valve; however, the check valves are not located in a position to prevent leakage of pressure when the valve member is shifted back to neutral and the structure of the patent includes specialized seat seal members which are necessary in addition to the check valves in order to assure the holding of pressure during movement of the valve member. Additionally, the seat seal members require a high overbalance of force to maintain the members against the valve plate.